This test is a measure of serum cortisol (also known as hydrocortisone), or urine cortisol, (also known as urinary free cortisol), an important hormone produced by a pair of endocrine glands called the adrenal glands.
This test is performed on patients who may have malfunctioning adrenal glands. Blood and urine cortisol, together with the determination of adrenocorticotropic hormone (ACTH), are the three most important tests in the investigationof Cushing's syndrome (caused by an overproduction of cortisol) and Addison's disease (caused by the underproduction of cortisol).
Increased levels of cortisol are associated with pregnancy. Physical and emotional stress can also elevate cortisol levels. Drugs that may cause increasedlevels of cortisol include estrogen, oral contraceptives, amphetamines, cortisone, and spironolactone (Aldactone). Drugs that may cause decreased levelsinclude androgens, aminoglutethimide, betamethasone, and other steroid medications, danazol, lithium, levodopa, metyrapone and phenytoin (Dilantin).
Cortisol is a potent hormone known as a glucocorticoid that affects the metabolism of carbohydrates, proteins, and fats, but especially glucose. Cortisolincreases blood sugar levels by stimulating the release of glucose from glucose stores in cells. It also acts to inhibit insulin, thus affecting glucose transport into cells.
The hypothalamus (an area of the brain), the pituitary gland (sometimes called the "master gland") and the adrenal glands coordinate the production of cortisol. After corticotropin-releasing hormone (CRH) is made in the hypothalamus, CRH stimulates the pituitary to produce adrenocorticotropic hormone (ACTH). The production of ACTH in turn stimulates a part of the adrenal glands known as the adrenal cortex to produce cortisol. Rising levels of cortisol act asa negative feedback to curtail further production of CRH and ACTH, thus completing an elaborate feedback mechanism.
There are two methods for evaluating cortisol: blood and urine. The most reliable index of cortisol secretion is the 24-hour urine sample collection, butwhen blood levels are required or requested by the physician, plasma cortisolshould be measured in the morning and again in the afternoon. Cortisol levels normally rise and fall during the day in what is called a diurnal variation, so that cortisol is at its highest level between 6-8 A.M. and gradually falls, reaching its lowest point around midnight. One reason for ordering bloodcortisol levels versus a 24-hour urine collection is that sometimes the earliest sign of adrenal malfunction is the loss of this diurnal variation, even though the cortisol levels are not yet elevated. For example, individuals withCushing's syndrome often have upper normal plasma cortisol levels in the morning and exhibit no decline as the day progresses.
When testing for cortisol levels through the blood, a blood specimen is usually collected at 8 A.M. and again at 4 P.M. It should be noted that normal values may be transposed in individuals who have worked during the night and slept during the day for long periods of time.
When testing for cortisol level through the urine, a 24-hour urine sample iscollected, refrigerated, and sent to the reference laboratory for examination.
Risks for the blood test are minimal, but may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, orhematoma (blood accumulating under the puncture site).
Reference ranges for cortisol vary from laboratory to laboratory but are usually within the following ranges for blood:
- Adults (8 A.M.): 6-28 mg/dL; adults (4 P.M.): 2-12 mg/dL
- Child 1-6 years (8 A.M.): 3-21 mg/dL;child 1-6 years (4 P.M.): 3-10 mg/dL
- Newborn: 1/24 mg/dL.
Reference ranges for cortisol vary from laboratory to laboratory but are usually within the following ranges for 24-hour urine collection:
- Adult: 10-100 mg/24 hr
- Adolescent: 5-55 mg/24 hr
- Child: 2-27 mg/24hr.
Increased levels of cortisol are found in Cushing's syndrome, excess thyroidhyperthyroidism), obesity, ACTH-producing tumors, and high levels of stress.
Decreased levels of cortisol are found in Addison's disease, conditions of low thyroid, and hypopituitarism, in which pituitary activity is diminished.